After the 1906 earthquake and its resulting fires destroyed much of San Francisco, public support surged for a reliable water supply, allowing the city to look beyond the Bay Area to meet the region’s growing need for dependable, high-quality water. The 1913 Congressional Raker Act authorized San Francisco to use the Tuolumne River in Yosemite National Park’s Hetch Hetchy Valley as a municipal water supply. Today, spring snowmelt from the Tuolumne River fills Hetch Hetchy Reservoir, the largest reservoir in the SFPUC water system, and gravity moves the water to over 2.7 million people. More than half flows to customers in Alameda, Santa Clara, and San Mateo Counties, while the rest is delivered to San Francisco or stored in local reservoirs such as Lower Crystal Springs. Lower Crystal Springs Dam on San Mateo Creek was constructed in 1888 using interlocking concrete blocks and, although adjacent to the San Andreas Fault, survived both the 1906 and 1989 earthquakes without significant damage.